This
overview is based on distinctions registered in Shetland Scots as of
the end of the 19th century by Jakob Jakobsen and presented in his
"Etymological Dictionary of the Norn Language in Shetland", v.I, p. LIX, with some additions.
Most of the features mentioned below are undoubtedly of Norn origin, although influences from Scots may also be seen in between. (Additions to this list are more than welcome.)